An example of how to set up Jenkins in a fully automated way

Jenkins is a self-contained, open source automation server which can be used to automate all sorts of tasks such as building, testing, and deploying software.

This project builds a Docker image that contains a fully configured Jenkins. Often, Jenkins is configured by hand. This has several problems:

• Over time, it becomes hard to understand how it was configured and why.
• Testing out configuration changes is difficult and often happens in production.
• The configuration must be backed up in case the machine the where the configuration is located crashes.

By completely automating the configuration of Jenkins:

1. The configuration is completely traceable and changes to the configuration can be tracked over time.
2. Configuration changes can be developed and tested locally.
3. A new instance of Jenkins spun up and configured within minutes.

How to start

docker run \
  --name auto-jenkins \
  --publish 8080:8080 \
  --detach \
  --restart always \
  scheleaap/jenkins-automation

In its default state, auto-jenkins has a single job called seed-job that creates the other jobs listed in the file job.groovy.override. Simply run the seed job to initialize the other jobs.

Once it is completed, you should see all jobs listed on auto-jenkins' dashboard. auto-jenkins should be ready to be used: run your newly added job and ensure Jenkins is behaving correctly.

See https://github.com/jenkinsci/docker#usage for more information and options.

How to configure Jenkins

All configuration is done using Groovy scripts located in src/main/resources/docker/init.groovy.d. Use the Jenkins Javadoc as a reference.

Environment variables

Some Groovy scripts use environment variables to make it easy to configure the container. The following table lists the most common environment variables.

Environment variable	Description
JENKINS_ADMIN_EMAIL	The admin's e-mail address
JENKINS_BASE_URL	The base URL of Jenkins
JENKINS_MASTER_EXECUTORS	The number of executors for the master
JENKINS_SLAVEPORT	Port for slaves to connect to
SMTP_HOST	SMTP server hostname
SMTP_PORT	SMTP server port number

How to add a new job

1. Clone the repository

   git clone [email protected]:scheleaap/jenkins-automation.git

2. Locate the file job.groovy.override and add your repository to the list of projectDefinitions.

How to add a plugin

Just modify the file plugins.txt file. See also https://github.com/jenkinsci/docker#preinstalling-plugins for more information.

How to build locally

mvn clean install -Plocal

Future work

Use Jenkins Configuration as Code: https://github.com/jenkinsci/configuration-as-code-plugin/blob/master/README.md

Literature

• Jenkins Job DSL API
• Pipeline Steps Reference
• Jenkins Javadoc